1. Sauce: In a blender, add prunes and hot water. Soak 5–10 minutes to soften prunes. Add garlic, ginger, soy sauce, mirin and sesame oil. Blend together until smooth.
2. Put steak in 5–7 litre slow cooker. Pour prune-soy blend over the steak and top with onion. Cover and cook on high for 4–5 hours.
3. Remove meat and place on cutting board. Skim any fat from the sauce surface, strain through a fine-mesh strainer into a saucepan and bring to a simmer.
4. In a small bowl, whisk together cornstarch and 1/4 cup water, then whisk into the sauce. Cook until sauce thickens and reduces down to about 500ml, about 5–10 minutes.
5. Rice bowl: Warm 1 tsp oil in a large skillet over medium-high heat. Add carrot and green onions, season with a pinch of salt. Cook, stirring frequently, until carrots are lightly browned. Transfer to a plate.
6. Warm 2 tsp oil in skillet. Add garlic and cook until aromatic, 1 minute. Add broccolini and a pinch of salt, cook, stirring often, until broccolini is lightly charred and crisp-tender, 3 minutes. Transfer to carrot plate.
7. Serve: Divide rice between bowls, place meat on top and spoon sauce over it. Top with sautéed vegetables and sesame seeds. Serve additional sauce and hot sauce on the side.

Tip: For a shortcut method, skim the braise in the final 20 minutes of cooking and add the carrots, green onions, and broccolini, allowing them to cook in the liquid instead of sautéing them separately. After slicing the meat, serve the vegetables and sauce directly from the slow cooker with rice.